Fossil of a legged snake rewrites the story of serpent evolution

A fossil discovered in Argentina has reshaped our understanding of snake evolution. Named Najash rionegrina, this ancient creature had well-developed legs, unlike most early snake fossils. Its discovery suggests that snakes once crawled before fully adapting to slithering.

In 2006, herpetologists Sebastián Apesteguía and Hussam Zaher described Najash in the journal Nature. The fossil, found in Argentine Patagonia, belonged to a Cretaceous snake with hips and hindlimbs—features absent in many other early snake remains. Unlike limbless snakes from marine environments, Najash had a pelvis firmly connected to its backbone, with legs extending beyond the ribcage.

A 2019 study in Science Advances later revealed that Najash and related species retained their legs for tens of millions of years. This challenges the idea that snakes lost their limbs all at once. Instead, forelimbs disappeared first, while hindlimbs persisted in some ancient lineages.

Scientists believe Najash's legs may have helped it burrow or grasp prey. Its existence alongside limbless snakes shows that both forms lived during the same period. As one of the earliest branches of Serpentes, Najash provides key clues about how snakes transitioned from crawling to slithering.

The discovery of Najash proves that early snakes were more diverse than previously thought. Its well-preserved legs and pelvis offer direct evidence of a gradual shift in snake anatomy. This finding forces researchers to rethink the timeline and process of limb loss in snake evolution.